A data printing apparatus employing an electrophotography method, e.g., a laser beam printer (hereinafter referred to as a “LBP”), is widely used as an output apparatus of a computer. Such data printing apparatus is the factor for rapid expansion of the field of desktop publishing by virtue of its many advantages such as high quality printing results, quietness, and high speed. Additionally, along with the sophistication of a host computer or a controller that serves as a printer's image generation unit, it has become easier to control color images, and color printers adopting an electrophotography method have been developed. As a result, conventional monochrome image printing, as well as color image printing is prevailing.
In a case where a color printer performs rendering, image data, such as a photograph image inputted by an image scanner or a digital camera, or color document data generated by an application program on a host computer, is subjected to color conversion processing using a color conversion parameter so as to match the color output characteristic of the printer. The color conversion parameter is data provided in the form of a matrix or look-up table (LUT).
When a color printer employing the electrophotography method converts RGB data to CMYK data, it is necessary to limit the amount of toner to a certain value due to the problem of fixing-ability and transferability. This limitation is imposed on the data value on which the color conversion has been performed. Particularly, in a case where printing data, such as CAD (computer-assisted design) data that places a great value on thin line reproducing ability, the limitation of the toner amount makes printing of a solid line impossible and may cause deterioration in the thin line reproducing ability. To solve this problem, there are several techniques available, such as an exposure control for actually performing the printing based on CMYK data, a control technique called PWM (pulse-width modulation), which adjusts the laser-driving pulse width in accordance with a data input value, can be used to ensure thin line reproducing ability while limiting the toner amount to a certain value. Pursuant to this technique, secondary colors such as red, green, or blue can be expressed with solid lines.
As described above, for data such as CAD data, which places a great value on thin line reproducing ability, the toner adhesion amount can be controlled by performing laser exposure control, i.e., PWM. However, in a case where the printing data is monochrome data, it is not necessary to perform multicolor printing, unlike full-color data, but it is ultimately the problem of fixability and transferability that is encountered, and is unrelated to the toner adhesion amount. If the aforementioned PWM processing is performed, the amount of the laser beam is reduced, causing declines in the overall density, and in some cases, the thin line reproducing ability deteriorates, causing problems.